Flutter BLoC mapEventToState gets called only the first time for an event and not called each next time that event is fired - flutter

Question

I have Courses and Tasks. Each Course has many Tasks. That is why I am using different screens in the app to show a list of courses and after a tap on a course, I am navigating to the next screen - a list of tasks. Here is my onTap method of the list of courses:
onTap: () {
TasksPageLoadedEvent pageLoadedEvent =
TasksPageLoadedEvent(
courseId: state.courses[index].id,
truckNumber: this.truckNumber,
);
serviceLocator<TaskBloc>().add(pageLoadedEvent);
Routes.sailor(
Routes.taskScreen,
params: {
Routes.courseNumber:
state.courses[index].courseNumber,
Routes.truckNumber: this.truckNumber,
Routes.courseId: state.courses[index].id,
},
);
}
I create a TasksPageLoadedEvent, pass it to the TaskBloc and navigate to the Tasks page.
Here is the TaskBloc and how it handles the mapping Event - State:
#override
Stream<TaskState> mapEventToState(
TaskEvent event,
) async* {
if (event is TasksLoadingEvent) {
yield TasksLoadingState();
} else if (event is TasksReloadingErrorEvent) {
yield TasksErrorState();
} else if (event is TasksFetchedFailureEvent) {
yield TaskFetchedStateFailureState(error: event.failure);
} else if (event is TasksPulledFromServerEvent) {
yield TasksPulledFromServerState(
truckNumber: event.truckNumber,
courseNumber: event.courseNumber,
courseId: event.courseId,
);
} else if (event is TasksPageLoadedEvent) {
yield TasksLoadingState();
final networkInfoEither = await this.getNetworkInfoQuery(NoQueryParams());
yield* networkInfoEither.fold((failure) async* {
yield TasksErrorState();
}, (success) async* {
if (success) {
final getTasksEither = await getTasksQuery(
GetTasksParams(
truckNumber: event.truckNumber,
courseId: event.courseId,
),
);
yield* getTasksEither.fold((failure) async* {
yield TaskFetchedStateFailureState(error: "coursesDatabaseError");
}, (result) async* {
if (result != null) {
yield TasksFetchedState(tasks: result);
} else {
yield TaskFetchedStateFailureState(
error: "coursesFetchFromDatabaseError");
}
});
} else {
yield TasksNoInternetState();
}
});
}
}
When I get navigated to the Tasks page, the BlocBuilder checks the state and handles the building accordingly. I have a Go Back functionality that navigates back to the Courses page:
onPressed: () {
serviceLocator<CourseBloc>().add(
CoursesPageLoadedEvent(truckNumber: this.truckNumber),
);
Navigator.of(context).pop(true);
},
This fires the similar event for the previous page and it gets re-loaded.
The problem I am facing happens if I want to go to another course and see its tasks. If I tap on another item in the list and therefore fire a new TasksPageLoadedEvent (with new properties) the mapEventToState() doesn't get called at all.
I have had similar issues with BLoC before, but they were regarding the BlocListener and states extending Equatable. That is why I had my events NOT extending Equatable (although I am not sure whether this was the issue here). But still nothing happens.
Here are my Events:
abstract class TaskEvent {
const TaskEvent();
}
class TasksPageLoadedEvent extends TaskEvent {
final String truckNumber;
final int courseId;
TasksPageLoadedEvent({
this.truckNumber,
this.courseId,
});
}
class TasksFetchedFailureEvent extends TaskEvent {
final String failure;
TasksFetchedFailureEvent({
this.failure,
});
}
class TasksLoadingEvent extends TaskEvent {}
class TasksReloadingErrorEvent extends TaskEvent {}
class TasksPulledFromServerEvent extends TaskEvent {
final String courseNumber;
final String truckNumber;
final int courseId;
TasksPulledFromServerEvent({
#required this.courseNumber,
#required this.truckNumber,
#required this.courseId,
});
}
How should I handle my back-and-forth between the two pages using two BLoCs for each page?

Answer 1

OK, I found an answer myself!
The problem, of course, as Federick Jonathan implied - the instance of the bloc. I am using a singleton instance created by the flutter package get_it. Which is really useful if you are implementing dependency injection (for a clean architecture for example).
So the one instance was the problem.
Luckily the package has implemented the neat method resetLazySingleton<T>.
Calling it upon going back resets the bloc used in that widget. Therefore when I navigate again to the Tasks page I am working with the same but reset instance of that bloc.
Future<bool> _onWillPop() async {
serviceLocator.resetLazySingleton<TaskBloc>(
instance: serviceLocator<TaskBloc>(),
);
return true;
}
I hope this answer would help someone in trouble with singletons, dependency injections and going back and forth within a flutter app with bloc.

Answer 2

for anyone else who has similar issue:
in case you are listening to a repository stream and looping through emitted object, it cause mapEventToState gets blocked. because the loop never ends.
Stream<LoaderState<Failure, ViewModel>> mapEventToState(
LoaderEvent event) async* {
yield* event.when(load: () async* {
yield const LoaderState.loadInProgress();
await for (final Either<Failure, Entity> failureOrItems in repository.getAll()) {
yield failureOrItems.fold((l) => LoaderState.loadFailure(l),
(r) => LoaderState.loadSuccess(mapToViewModel(r)));
}
});
}
what you should do instead of await for the stream, listen to stream and then raise another event, and then process the event:
watchAllStarted: (e) async* {
yield const NoteWatcherState.loadInProgress();
_noteStreamSubscription = _noteRepository.watchAll().listen(
(failureOrNotes) =>
add(NoteWatcherEvent.notesReceived(failureOrNotes)));
},
notesReceived: (e) async* {
yield e.failureOrNotes.fold(
(failure) => NoteWatcherState.loadFailure(failure),
(right) => NoteWatcherState.loadSuccess(right));
},